Electrolytic cell cover

ABSTRACT

AN ELECTROLYTIC CELL IS PROVIDED HAVING A COVER OF A MATERIAL WHICH WILL CONDUCT AN ELECTRIC CURRENT, THE UNDERSURFACE OF SUCH COVER BEING FORMED OF A REFACTORY MATERIAL SUBSTANTIALLY ENTIRELY EXCEPT FOR ALLOWING CONTACT OF THE ANODES OR ANODE STEMS WITH THE CURRENT CARRYING MATERIAL. A COVER OF SUCH CONSTRUCTION ALLOWS FOR SUBSTANTIALLY LESS LOSS OF HEAT FROM THE ELECTROLYTIC CELL AND SUBSTANTIALLY LESS WEAR AND MECHANICAL FAILURE DUE TO EXCESSIVELY HIGH TEMPERATURES OF THE COVER MATERIAL.

ELECTROLYTIC CELL COVER Filed Oct. 24, 1968 INVENTOR GEORGE G. DAY

3,556,974 ELECTROLYTIC CELL COVER George Gerald Day, New York, N.Y.,assignor to F. Barry Haskett, New York, N.Y. Filed Oct. 24, 1968, Ser.No. 770,255 Int. Cl. C22d 3/ 02-; Btllk 3/02 US. Cl. 204-243 4 ClaimsABSTRACT OF THE DISCLOSURE The present invention relates to animprovement in the construction of electrolytic cells and the coverthereof in particular; and more particularly, the present in ventionrelates to a new construction of the cover of the anode section of anelectrolytic cell of the horizontal type useful in the electrolysis offused salts wherein said cover comprises an electric current conductingmaterial, the inner surface thereof being covered with a refractorycomposition.

The present invention is particularly applicable to the construction ofcells which provide for the electrolysis of molten inorganic compoundsat high temperatures wherein a molten metal is employed as a cathode.Cells of this type operating with an electrolyte of fused salts havebeen known for some time. Thus, the examples of such cells include theAcker 'cell e.g., as described in US. Pat. 674,691, the Ashcroft celle.g., as disclosed in US. Pat. 1,159,154, the Hamprecht cell used inGermany during World War H and described in FIAT Report No. 830, as wellas the early Szechtman cell as represented by US. Pat. 3,104,213. Incells of this type, the top or cover is necessarily subjected tosubstantially the same temperature as that of the molten inorganiccompound employed as the electrolyte. Generally, temperatures in excessof 1300 F. and sometimes in excess of 1800 F. are employed, suchtemperatures being necessary to keep the electrolyte in a molten state.Accordingly, the top or cover of such horizontal electrolytic cells aresubjected to stress at the high temperatures to which they aresubjected, such stress generally resulting in a shortened life of thecover or top due to failure. Thus, the conventional cover materials tendto become mechanically weak and lose the dimensional stability. In arecent patent to Szechtman e.g., US. Pat. 3,235,479, itis proposed toemploy graphite as the cell cover of the horizontal electrolytic cell asthe type discussed above. While the graphite cover of such patent doesconduct an electric current, it is not a good conductor. Moreover,however, such graphite is an excellent conductor of heat therebyproviding for a great loss of heat through the cover of the electrolyticcell. On an industrial scale therefore, the use of graphite as the coverfor the horizontal electrolytic cell is disadvantageous in that itprovides for poor conduction of an electrical current while providing anexpensive loss of heat to the surround ang atmosphere. Accordingly, suchuse of the graphite cover has not solved the problem associated with theinherent disadvantages and deficiencies of cover and top materialsemployed in horizontal electrolytic cells such as embodied by thepresent invention, but, in fact, has tended to compound the same.Accord- United States Patent ingly, it has still been the desire of theindustry to provide a simple and eflicient cover for horizontalelectrolytic cells employing high temperatures in an electrolyticprocess especially adapted for the electrolysis of molten electrolytesutilizing a molten metal cathode.

Such inherent disadvantages and deficiencies of the prior art have beenovercome in accordance with the present invention wherein a cover forthe electrolytic cell is provided comprising a metal shell with arefractory lining, such refractory lining carrying connections therethrough to electrically conducting cover from the anodes. The use ofsuch a cover allows for the utilization of a metal shell capable ofcarrying the electric current necessary for operation of theelectrolytic cell, while the refractory lining present on the innersurface of the metal shell provides protection against excessive heatand heat loss to the atmosphere.

Accordingly, it is the principal object of the present invention toprovide an improvement in the production of covers for electrical cells,particularly of the horizontal type wherein a molten electrolyte isemployed in conjunction with the flowing molten metal cathode, suchimprovement eliminating the inherent deficiencies and disadvantagesassociated with the employment of prior art apparatus.

A further object of the present invention comprises an improvement inthe cover for a horizontal electrolytic cell wherein such covercomprises an electrically conducting metal shell containing a refractorylining, such refractory lining allowing contact between the anodes oranode stems and the metal shell.

A still further object of the present invention comprises a cover forthe electrolytic cell which eliminates the problem of fatigue andmechanical Weakness and loss of dimensional stability associated withthe high temperatures developed in the electrolysis process as Well asan excessive loss of heat to the atmosphere, the elimination of suchproblems being associated with the provision of a cover comprising ametal shell capable of conducting electricity necessary for theoperation of the electrolytic cell and as a lining therefore, arefractory material which resists degradation or deformation due to hightemperature and resists the passage of heat therethrough.

Still further objects and advantages of the novel improved electrolyticcell cover of the present invention will become more apparent in thefollowing more detailed description thereof in conjunction with theaccompanying drawings: wherein,

FIG. 1 is a side cross-sectional view of the cover of the presentinvention;

FIG. 2 is a cross-sectional view of an electrolytic cell having in placethe cover of the present invention.

In the figures, like numerals represent like elements.

In FIG. 1, the electrolytic cell cover of the present invention is shownas comprising a metal shell 1, containing a refractory liner 6,generally comprising a depth of 6 to 8" or more below the metal shell.The refractory liner 6, is generally of a castable or monolithicrefractory, such refractory liner 6 underlying approximately 60 to 90%,preferably -85% of the total cover area. The remainder of the cover areai.e. 10-40%, preferably 15- 20% is not covered by the castable ormonolithic ,refractory liner 6, so as to provide contact with the anodestems 7, of the electrolytic cell as will be discussed in more detail inreference to FIG. 2. Thus, while the heat from the electrolytic cellwill be conducted through that portion of the cover area not underlayedby the refractory lining, since such area comprises only a very minoramount of the total cover area i.e. only about 15- 20% of the totalarea, the heat conducted through this area will not be appreciable, inthis respect, since the refractory lining 6, is a poor conductor ofheat, comparatively little heat will be conducted through this areawhich underlays the major portion of the total cover area i.e. fromabout 60-90% of the total cover area. It is pointed out with respect tothe percentages of area covered and uncovered by the refractory lining 6as set forth above that such percentages are merely exemplary of atypical electrolytic cell embodying the present invention. Of course,where desired for particular purposes it may be desirable to underlaymore or less of the total cover area with the refractory liningdepending in part on the area necessary for the contact of the anodestem and bushings with the electrically conducting metal shell and, theamount of heat which can be tolerated by the metal shell itself. Sincethe heat transmitted through the area of the cover above the anodes i.e.that area not underlayed by the refractory lining 6, together with thecomparatively small amount of heat transmitted through the refractorylining 6 itself, will be dissipated over the whole area of the cover,the cover material i.e. the metal shell will be generally maintained ata moderate temperature which can be tolerated by any and all of themetals employed which are capable of conducting the electric currentnecessary for operation of the electrolytic cell.

While any material having the requisite characteristics of ability toconduct electricity and resistance to the temperatures to which themetal shell is heated can be employed, it is preferred that the metalshell 1 of the cover comprise a nickel-clad mild steel with thenickel-clad surface facing downward. The nickel-clad mild steel ispreferred since nickel most effectively resists the action of drychlorine gas up to a temperature of about 1000 F. whereas straight steelresists such dry chlorine gas up to a temperature of about 300 F. Thus,although this is a consideration in selecting the metal for use in thecover of the elctrolytic cell of the present invention, it is pointedout that contact with the chlorine gas and other products and reactantsof the electrolysis reaction is minimized by the fact that a substantialproportion of the undersurface of the metal shell is underlayed with afairly substantial refractory liner 6. However, while various alloys ofsteel etc. have the requisite characteristics for use in accordance withthe present invention, the use of the nickel-clad mild steel ispreferred for the reasons set forth above.

Again, it is pointed out that in View of the fact that the metal shellof the cover does not achieve an extremely high temperature and is notcontacted by the reactants and products of the electrolysis because ofthe refractory liner 6, the mostesseutial characteristic of the metalemployed for the shell is that it be a good conductor of electricity.

As indicated previously, the refractory lining preferably comprises acast or monolithic refractory material. Such materials generally arefairly inert to the environment of the electrolytic cell and inaddition, possess the necessary property of not allowing passage ofsubstantial amounts of heat. In other words, the refractory liningsemployed in accordance with the present invention are poor conductors ofbeat, this commoncharacteristic of all applicable and conventionalrefractories allowing the same to be operably employed in theelectrolytic cell cover of the present invention. Thus, suitablerefractories ha ving the requisite relatively low co-efficient of heattransfer include those which have a high percentage of alumina ormagnesia. Thus, a cement refractory composition may suitably employcalcium aluminate as a binder. High silicate content refractories arenot preferred since, especially when a sodium salt e.g., sodium chlorideis electrolized in the electrolytic cell, the sodium present has theeffect of reducing the silica content. In addition to the alumina and/ormagnesia content or other refractory materials, the refractory lining ofthe electrolytic cell cover of the present invention can include asuitable filler material e.g., vermiculite, crushed firebrick, etc.

As indicated previously, almost any conventional refractory material canbe employed with the present invention, the sole requirement forsuitability being a relative inertness to the atmosphere of theelectrolytic cell and, a fairly low coefficient of heat transfer, so asto be a poor conductor of heat.

The cover of the present invention, comprising the metal shell 1 andrefractory liner 6, is shown in FIG. 2 in a conventional elctrolyticcell. The inside surface of the metal shell 1 of the cover is providedwith anchors or studs 4 extending into the body of the refractory linerto provide a mechanical bond between the refractory liner 6 and metalshell 1. While such anchors or studs 4 are not essential since both therefractory liner 6 and metal shell '1 can be adequately supported by thesides of the electrolytic cell, the use of such anchors or studs 4provides a more cohesive structure by providing the mechanical bondbetween the portions of the cover.

As shown in FIG. 2, the electrolytic cell can also contain atop thecover a water jacket of any conventional design. The water jacket 2assists in lowering the temperature of the cover still further thanpossible by the use of the refractory liner alone.

In the electrolytic cell represented in FIG. 2, graph ite anode stems 7are screwed into nickel bushings 9 which are connected to the metalshall 1 of the cover but do not pass therethrough. The anodes 8 of thetype similar to those employed in mercury-alkali chloride cells, e.g.,graphite anodes, are pressed onto the lower ends of the anode stems 7.Generally the nickel bushings 9 with internal threads so as to bereceptive to the anode stems 7 are welded to the metal shell 1 of thecover of the electrolytic cell in any suitable manner.

As shown in FIG. 2, the interior of the electrolytic cell may be linedwith carbon or graphite slabs 5, which slabs provide additionalprotection of the cell construction against the action of chlorine gas.

In the operation of the electrolytic cell the current enters the cellfrom a bus (not shown) connected to lead 13 which is bolted or otherwisefastened to the metal shell 1 of the cover, preferably extending beyondthe exterior of the electrolytic cell as shown in FIG. 2. The currenttravels through the metal shell 1, through the nickel bushings 9,through the anode stem 7 to the anode proper 8. From the anode 8 thecurrent passes through the fused salt electrolyte 15 to the cathode 16,generally a molten metal such as lead, tin or an alloy, for example, alead-sodium alloy. The current passes from the cathode 16 to the cellbottom 17 and then to connection 14 leading to the negative bus (notshown).

While not illustrated in FIG. 2, the cell bottom of the electrolyticcell to which the improved cell cover of the present invention is mostapplicable is preferably of the type disclosed in co-pending applicationSer. No. 542,002, filed Apr. 12, 1966, now US. 3,468,786. Such cellbottom as defined in such co-pending application comprises a metal baseand a relatively fixed refractory overlayer disposed on top of the base,the refractory overlayer having at least one recess extending fullythrough its thickness so as to permit direct contact between the metalbase and the flowing molten cathode. As is the case with the refractoryunderlayer employed in accordance with the improved cell of the presentinvention the refractory employed in conjunction with the cell bottom asillustrated in applicants co-pending application is characterized byhaving a low co-efiicient of heat transfer.

As indicated previously, the improved cell cover of the presentinvention is most applicable to a horizontal cell adapted for theelectrolytic decomposition of inorganic compounds at highly elevatedtemperatures. Such inorganic compounds comprising the electrolyteemployed in the electrolysis process generally comprise fused halides ofalkali metals, e.g., sodium chloride, potassium chloride and lithiumchloride as well as the halides of alkaline earth metals, etc., e.g.,calcium chloride, etc.

Such a horizontal cell to which the improved cell cover of the presentinvention is most applicably adapted generally comprises as shown inFIG. 2 a substantially horizontal bottom surface, side walls, anodes inspace relationship to and disposed above the bottom and means separatelyelectrically connected to the anodes from the cell cover and to thebottom of the electrolytic cell adapted to pass electric current fromthe anodes to the bottom through a flowable molten metal cathode,generally molten lead. In such an electrolytic cell the molten inorganiccompound, e.g., electrolyte floats on the cathode in contact with theanodes. Generally in such electrolytic cells the cell bottom has aslight slope so as to permit the molten metal cathode, e.g., lead, tofiow across the bottom from one end of the cell to the other.

As noted previously, such an electrolytic cell is shown in a recentlyissued patent to Szechtman, US. Pat. 3,235,479. In accordance with suchpatent, however, the cell cover is prepared from a material whichconducts electricity, e.g., graphite. The structure illustrated in thatpatent, however, has been greatly improved in accordance with thepresent invention by providing a cell cover which comprises incombination a metal shell capable of conducting electricity and arelatively thick underlayer of a refractory material having a relativelylow coefficient of thermal conductivity and allowing direct contact ofthe anodes with the metal shell through anode stems and bushings, e.g.,preferably nickel bushings.

Thus, while the present invention has been described in respect to theforegoing exempli-fication as embodied by FIGS. 1 and 2, it is to beunderstood that the present invention is in no way to be limited theretobut must be construed as broadly as are any equivalents thereof.

I claim:

1. In a horizontal electrolytic cell adapted for electrolyticdecomposition of inorganic salt electrolytes at high temperaturescomprising a substantially horizontal bottom surface, side walls,current-carrying cover, anodes in spaced relationships and connected tosaid cover to receive electric current therefrom, said bottom surfacebeing adapted to support said inorganic salt electrolyte floating on amolten metal cathode, said electrolyte being in contact with said anodesso that electric current passes through said electrolyte to saidcathode, the improvement which comprises a cover comprising a metalshell capable of carrying an electric current and a relatively thickrefractory underlayer thereof, said refractory underlayer comprising asubstantial portion of the underside of said metal shell but allowingelectrical contact between said metal shell and anodes, said refractorybeing characterized by a relatively low coefficient of heat transfer.

2. The horizontal electrolytic cell of claim 1 wherein said refractoryunderlays from about 60-90% of said metal shell.

3. The horizontal electrolytic cell of claim 1 wherein anchoragesprovide mechanical adhesive between said metal shell and refractoryunderlayer.

4. The horizontal electrolyte cell of claim '1 where said refractoryunderlayer comprises predominantly alumina. or References Cited HOUNITED STATES PATENTS 1,782,616 11/1930 Hulin 204-243 2,950,236 8/1960Dean et al. 204-243X 3,235,479 2/ 1966 Szechtman 204-243 30 FOREIGNPATENTS 5,648 6/ 1906 Great Britain 204-246 542,886 1/ 1942 GreatBritain 204-243 35 JOHN H. MACK, Primary Examiner D. R. VALENTINE,Assistant Examiner US. Cl. X.R.

